1. Field of the Invention
The present invention relates to a sealing device and a sliding member.
2. Description of Related Arts
To make sliding resistance between two objects which slide over each other as low as possible is an extremely important objective to mechanical components such as a bearing and a seal. The reason for this is that it can not only contribute to the improvement in the life of the mechanical components but also restrains the loss of energy.
Conventionally, a surface of a sliding portion has been coated with fluorocarbon resin which is a low friction resin. However, the fabrication cost is increased. Further, a lubricant such as grease or lubricating oil has been interposed between two objects. However, the lubricant may, in some cases, run out. Therefore, there is a limit to the reduction in sliding resistance.
Meanwhile, in a sliding portion constructed using a high polymer material, sliding resistance is generally liable to be increased. A sealing device for sealing a space between a rotating axis and a housing and a space between a reciprocating axis and the housing, for example, has a sliding portion composed of a rubber material which slides to and from the rotating axis and the reciprocating axis. However, the sliding resistance may, in some cases, be increased by running out of an oil film of the sliding portion.
In one, used for a clutch in an automatic transmission of an automobile, for example, of the above-mentioned sealing devices, an annular sealing member made of rubber is generally provided on the inner periphery and the outer periphery of a piston member, and a surface of the sealing member is provided with a lip serving as a sliding portion brought into contact with the housing. Consequently, a space between the housing and the piston member is sealed.
Conventionally, the lip of the sealing member has its whole sliding surface brought into contact with the housing or the like, so that the sliding resistance is high. Moreover, sealing members are respectively provided on the inner periphery and the outer periphery of the annular piston member. Accordingly, the response characteristics of the operation of the piston member are poor.
On the other hand, a sealing device in which a sliding surface of a lip is provided with an annular projection or the like along its circumference has been proposed (e.g., JP-A-9-210088) for the purpose of reducing sliding resistance. However, the sliding resistance is not sufficiently reduced.